Mini-Split Error Code or Blinking Light? What It Means and What to Do
The indoor unit shows a code or flashes a light, and the system stops or won't cool.
By Mark Curant·Updated
Most likely causes
- A power glitch or surge that left the control board locked out (a reset often clears it)
- Dirty filters or a blocked outdoor unit, so the system shuts down to protect itself
- A communication error between the indoor and outdoor units (wiring, a surge or a board)
- A failed temperature sensor (thermistor)
- A drain or condensate pump problem on units with a float switch
- Low refrigerant
- A fault in the outdoor unit's inverter board or compressor
Before you open anything
Turn the system off at the thermostat, then switch off power at the breaker and at the disconnect beside the outdoor unit. Never touch the capacitor, even with the power off: it can hold a dangerous charge. Refrigerant work is for licensed technicians only. Reset a tripped breaker once; if it trips again, leave it off.
Don't open the outdoor unit's covers. Mini-split outdoor units contain inverter boards with capacitors that stay charged at high voltage for several minutes after the power is off.
Check these first (free, 5 minutes)
- Write the code down exactly, or count the blinks: how many, which light (often Operation or Timer), and whether the pattern repeats. A short phone video helps.
- Find your exact model numbers on the labels of the indoor and outdoor units. Codes differ between brands and even between a brand's own product lines.
- Look it up in the owner's or installation manual for that model (most are on the manufacturer's website). Some units also have a code list on a label inside the front panel or the outdoor unit's service cover.
- Check the filters behind the front panel, and make sure nothing blocks the outdoor unit.
Causes, signs and repair costs
Power glitch or lockout
DIYCode appeared after an outage, storm or flicker
Typical cost: $0 (reset)
Dirty filters or blocked outdoor unit
DIY or proProtection codes for high temperature or pressure, or freeze protection; dusty mesh filters
Typical cost: $0 to clean filters, $100–$300 pro cleaning
Communication error
ProIndoor and outdoor units can't talk to each other. Common examples: U4 on many Daikin units, E6 on many Mitsubishi units
Typical cost: $75–$200 service call plus wiring or a board
Failed temperature sensor
ProSensor or thermistor code; unit stops or runs oddly
Typical cost: $75–$200 service call plus the sensor
Drain or condensate pump problem
DIY or proWater dripping from the indoor unit; float or drain code
Typical cost: $75–$200 drain clearing, $150–$400 pump
See: AC leaking water →Low refrigerant (a leak)
ProWeak cooling, ice on the lines, low-pressure or refrigerant code
Typical cost: $400–$2,400 to find, fix and recharge
Inverter board or compressor fault
ProOutdoor unit code that returns after every reset
Typical cost: $75–$200 plus the board (often several hundred dollars); $1,500–$3,000 for a compressor
| Cause | Signs | Who fixes it | Typical cost |
|---|---|---|---|
| Power glitch or lockout | Code appeared after an outage, storm or flicker | DIY | $0 (reset) |
| Dirty filters or blocked outdoor unit | Protection codes for high temperature or pressure, or freeze protection; dusty mesh filters | DIY or pro | $0 to clean filters, $100–$300 pro cleaning |
| Communication error | Indoor and outdoor units can't talk to each other. Common examples: U4 on many Daikin units, E6 on many Mitsubishi units | Pro | $75–$200 service call plus wiring or a board |
| Failed temperature sensor | Sensor or thermistor code; unit stops or runs oddly | Pro | $75–$200 service call plus the sensor |
| Drain or condensate pump problemSee: AC leaking water → | Water dripping from the indoor unit; float or drain code | DIY or pro | $75–$200 drain clearing, $150–$400 pump |
| Low refrigerant (a leak) | Weak cooling, ice on the lines, low-pressure or refrigerant code | Pro | $400–$2,400 to find, fix and recharge |
| Inverter board or compressor fault | Outdoor unit code that returns after every reset | Pro | $75–$200 plus the board (often several hundred dollars); $1,500–$3,000 for a compressor |
Typical U.S. installed prices in 2026. Most repairs also carry a service call fee of $75–$200, often credited toward the repair. See AC repair costs in 2026 for the full list.
Step by step
- 1
Record the code
Note the code or blink pattern, the time, the mode (cool, heat, dry) and what the unit was doing. Take a photo or short video.
- 2
Look it up for your exact model
Use the model numbers from the unit's labels to find the manual. Generic online lists often conflict, because the same code can mean different things on different product lines.
- 3
Reset once
Turn the unit off with the remote, switch off its breaker or outdoor disconnect, wait about 5 minutes, then restore power and restart with the remote. If the code comes straight back, stop resetting it.
- 4
Clean the filters and clear the outdoor unit
Lift the front panel, slide out the mesh filters and rinse them in lukewarm water. Let them dry fully before refitting. Outside, clear leaves, snow or plants away from the unit.
- 5
Rule out the normal blinks
In heating mode, many mini-splits blink a light while the outdoor unit defrosts, and stop after several minutes. Some also blink while they warm up. Check the remote's batteries and mode too.
- 6
Call with the details
Give the technician the brand, both model numbers, the exact code, when it started and what you have tried. They can often tell which part to bring.
Call a technician if
- The code comes back after one reset
- A communication, sensor, inverter or compressor code
- Water dripping from the indoor unit
- Ice on the copper lines
Red flags on a quote
- A new system quoted for a communication error before the connecting wiring and terminals are checked
- A board replaced without explaining what the code and the test readings showed
- A refrigerant recharge with no leak search
Facing an expensive repair on an older system? Run it through the repair vs replace calculator, or read the $5,000 rule.
Frequently asked questions
What does a blinking light on my mini-split mean?
Usually that the unit has detected a fault and stopped. The number of blinks, and which light blinks, is a code you can look up in the manual for your exact model. In heating mode, a blinking light can also just mean the unit is defrosting, which is normal and stops after several minutes.
How do I reset a mini-split error code?
Turn the unit off with the remote, switch off its breaker or outdoor disconnect for about 5 minutes, then turn the power back on and restart it with the remote. If the code returns, don't keep resetting: the fault is still there.
What is a communication error on a mini-split?
It means the indoor and outdoor units can't exchange signals. Causes include loose or corroded connecting wires, a surge that damaged a board, or a failed board. On many Daikin units it shows as U4, and on many Mitsubishi units as E6, but check your manual: codes vary by model.
Can I trust mini-split error code lists online?
Use them as a starting point only. Codes differ between brands and between product lines from the same brand, and generic lists often disagree. The manual for your exact model number, or the manufacturer's support line, is the reliable source.
Related problems
AC not working after a power outage
Power is back on, but the AC won't start or doesn't cool.
AC leaking water
Water around the indoor unit, a dripping ceiling or a full drain pan.
AC frozen up
Ice on the copper lines or indoor coil, weak airflow, water as it melts.
Fixed it? Check what it costs to run
If your system is old enough to keep breaking, compare its running cost with a new one before the next repair.
Open the SEER savings calculator